have created a guarded block over the entire document. RangeMarker rangeMarker = document.createGuardedBlock(0, document.getTextLength()); rangeMarker.setGreedyToLeft(true); rangeMarker.setGreedyToRight(true); I expect this document not to be editable any more. Yet if the cursor is at the beginning or at the end of the document, I am still able to change it. The newly introduced character(s) will be part of the readonly RangeMarker, which is an additional misbehavior.